1. Technical Field
The present invention relates to a method of purifying yellow phosphorus, and more particularly, to a method of effectively removing impurities from yellow phosphorus used as raw materials of a phosphoric acid to increase purity of the phosphoric acid, the method including: removing impurities from the phosphoric acid by adding an oxidizing agent to the yellow phosphorus, followed by stirring; and removing impurities by adding a solution including an additive having a specific functional group in a chemical structure to the yellow phosphorus from which the impurities are removed, followed by stirring.
2. Description of the Related Art
Phosphoric acid is used to remove a silicon nitride film deposited on a semiconductor wafer, or metal wiring etching of a display such as a thin film transistor-liquid crystal display (TFT-LCD). In the semiconductor, the phosphoric acid is mainly used in a form in which pure phosphoric acid is mixed with an additive. In the TFT-LCD, the phosphoric acid is mainly used in a form in which a mixed acid including various kinds of acids such as a phosphoric acid, a nitric acid, an acetic acid, and the like, is mixed with the additive.
A method of producing the phosphoric acid may be largely classified into two ways.
That is, there are 1) a wet method of using a solution during the production, and 2) a dry method of adding water at the end of the production.
Among them, in the dry method, the phosphoric acid is produced by oxidizing and combusting yellow phosphorus (P4) which is a raw material to form an oxide dimer (P4O10) of phosphorus pentoxide (P2O5), and adding water thereto. Unlike the wet method, the dry method has an advantage in that significantly high concentration of phosphoric acid having 80 to 90 mass % is capable of being produced by controlling an amount of water to be added at the end of the production.
The dry method is beneficial in view of the production cost since the method is not complicated; however, has a problem in that purity of the yellow phosphorus as the raw material has a direct effect on purity of phosphoric acid to be produced.
The yellow phosphorus (P4) being a raw material of the phosphoric acid is present in nature in the form of ore. Upon analyzing the yellow phosphorus after mining, the yellow phosphorus includes large amounts of arsenic and antimony included in the same group as the periodic table, together with phosphorus, and large amounts of metal impurities such as iron, aluminum, and the like.
In order to produce a high purity of phosphoric acid, methods of purifying the raw material yellow phosphorus while utilizing the advantages of the drying method as described above have been developed.
Regarding this, Japanese Patent Laid-Open Publication No. Sho 60-016368 discloses a method of purifying phosphorus, specifically, a method of separating impurities oxidized by an mixed acid including: mixing 6-18 mass % of nitric acid and 15-38 mass % of sulfuric acid at a molar ratio of 1:1 to 1:4, and treating yellow phosphorus with a mixed acid having a concentration of all acids (molar concentration of nitric acid+molar concentration of sulfuric acid) in the range of 3.5 to 6.5 moles at 45 to 100° C.
In addition, U.S. Pat. No. 6,146,610 discloses a method of removing arsenic from an element, phosphorus, specifically, a method of treating phosphorus with oxidized iodine including: mixing an appropriate amount of iodine with hydrogen peroxide and removing arsenic present in the phosphorus at a temperature of 45 to 95° C. under condition in which an amount of the oxidizing agent is no more than 10 mass % as active oxygen relative to weight of the phosphorus.
Further, Korean Patent Laid-Open Publication No. 2012-0005960 discloses a method of producing high purity elemental phosphorus and a method of producing high purity phosphoric acid, specifically, a method of simultaneously removing antimony and arsenic by contacting an iodic acid-containing compound such as an iodic acid, an iodate, and the like, with phosphorus, to be oxidized, and reacting the obtained oxide with a chelating agent.
Further, Japanese Patent Laid-Open Publication No. Hei 06-040710 discloses a method of producing high purity phosphorus, specifically, a method of removing impurities by converting arsenic into arsenite using oxidized iodine and iodic acid compound in order to remove arsenic in yellow phosphorus, followed by distillation.
However, these methods according to the related art have problems as follows.
Most of the methods for purifying impurities from the yellow phosphorus used as the raw material are an oxidization method using an oxidizing agent, wherein the oxidizing agent to be used is a strong acid such as a sulfuric acid, a nitric acid, an iodic acid, or the like.
That is, the methods according to the related art have a core constitution of purifying the yellow phosphorus, including liquefying the yellow phosphorus most of which has a melting temperature of 44.1° C. by increasing a temperature, stirring the phosphorus with materials including the oxidizing agents, to oxidize the impurities such as antimony, arsenic, and the like, and removing oxidized impurities.
However, the raw material yellow phosphorus is possible to be changed into phosphorus pentoxide, wherein the phosphorus pentoxide reacts with water present in a reaction solution to be phosphoric acid, resulting in loss of the raw material yellow phosphorus.
In fact, upon reviewing Examples of Japanese Patent Laid-Open Publication Sho 60-016368 among the above-described related art documents, it may be appreciated that a mass of the raw material yellow phosphorus is reduced from 20 g to 13 g after purification, and a yield is about 70%, which is significantly low.
Meanwhile, since iodine compounds have significantly strong oxidizing power, the method of using iodine, iodide or iodic acid is capable of effectively removing impurities such as antimony, arsenic, and the like. However, the iodine is a hazardous material, and has difficulty in treatment during the production, and has a problem in waste water treatment after being reacted. Further, since other side reactions may proceed due to iodide ions that may remain in the raw material yellow phosphorus, remaining iodide ions are required to be confirmed.
Therefore, a method capable of effectively removing metal impurities such as antimony, iron, aluminum, and the like, from the yellow phosphorus as the raw material of phosphoric acid, without having the above-described problems, has been required to be developed.